No abstract

The influence of the support material of vanadia catalysts on the reaction rate, activation energies, and defect formation enthalpies was investigated for the oxidative dehydrogenation of ethanol and propane. Characterization by infrared absorption–reflection spectroscopy (IRAS), Raman and UV–vis spectroscopy verifies a high dispersion of vanadia for powder and thin-film model catalysts. The support effect of ceria, alumina, titania, and zirconia is reflected in activation energy, oxidative dehydrogenation (ODH) rate, and temperature-programmed reductions (TPR) for both catalyst systems, ethanol and propane. Impendence spectroscopy and density functional theory (DFT) calculations were used to determine the defect formation enthalpy of the vanadyl oxygen double bond, providing the scaling parameter for a Bell–Evans–Polanyi relationship. On the basis of a Mars–van-Krevelen mechanism, an energy profile for the oxidative dehydrogenation is proposed

No abstract

Li-doped MgO was prepared on different preparative routes and with different loadings. The catalytic activity was found to decay for all catalysts for 40 h time on stream. A detailed structural analysis of 0.5 wt% Li-doped MgO showed heavy losses of Li, reduced surface area and grain growth. A correlation between these factors and the deactivation could not be found. The reaction temperature and the flow rate were found to be the main deactivation parameters.

Current light microscopic methods such as serial sectioning, confocal microscopy or multiphoton microscopy are severely limited in their ability to analyse rather opaque biological structures in three dimensions, while electron optical methods offer either a good three-dimensional topographic visualization (scanning electron microscopy) or high-resolution imaging of very thin samples (transmission electron microscopy). However, sample preparation commonly results in a significant alteration and the destruction of the three-dimensional integrity of the specimen. Depending on the selected photon energy, the interaction between X-rays and biological matter provides semi-transparency of the specimen, allowing penetration of even large specimens. Based on the projection-slice theorem, angular projections can be used for tomographic imaging. This method is well developed in medical and materials science for structure sizes down to several micrometres and is considered as being non-destructive. Achieving a spatial and structural resolution that is sufficient for the imaging of cells inside biological tissues is difficult due to several experimental conditions. A major problem that cannot be resolved with conventional X-ray sources are the low differences in density and absorption contrast of cells and the surrounding tissue. Therefore, X-ray monochromatization coupled with a sufficiently high photon flux and coherent beam properties are key requirements and currently only possible with synchrotron-produced X-rays. In this study, we report on the three-dimensional morphological characterization of articular cartilage using synchrotron-generated X-rays demonstrating the spatial distribution of single cells inside the tissue and their quantification, while comparing our findings to conventional histological techniques.